Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TITI.E
Food Package for Microwave Cooking
~CKGROUND OF THE I~VENTION
Field Q~_~he Invention
This invention relates to a food package .in
which food resting on a grease-absorbing pad can be
cooked directly in the package by microwave energy. More
particularly, ~he invention concerns an improvement-in
such a package where.in the grease-absorbing pad is a
composite nonwoven fabric comprising a porous spunbonded
polyester outer fabric at~ached to a naedle-punched
nonwoven polyester staple-fiber web.
Description of tbe Prior Art
Packages are known for use in microwave cooking
of foods that generate large amounts of liquid grease,
fat and oil. In such packages, the food usually rests on
a grease-absorbing pad and is sealed in a
~icrowave-transparent film enclosure.
Larson, U. S~ Patent 4,865,85~, and Larson
et al, U. S. Patent 4,~73,101, disclose such food
packages for microwave cooking of bacon, sausages, and
other such fatty foods. The food rests on a pad of
melt-blown microfibers of polypropylene,
poly(4-methylpentene-1~, polyethylene, polyester, or a
mixtures thereof, preferably a 50J50 mixture of
polypropylene and polymet~ylpentene. The pad has a
network o~ compacted high-density regions and low-density
pillowed regions. Grease that is liquefied and released
from the food during cooking is absorbed by the pad and
amounts to 4 to 12 times the weigh~ of the pad. The food
and pad are contained in a vapor-tight enclosure that is
transparent to microwaves and visible light.
Mon~orten et al, U. S. Patent 4,786,513, and
Lunquist et al, U. S. Patent 4,720,410, each disclose a
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food package for microwave cooking of stacked slices of
bacon. Sheets in~terleaved between successive strips of
bacon direct the liquid greas~ that forms during cooking
to an absorbent ~lotter. The blotter consists of a
perforated thermoplastic film atop a grease-absorbing
layer of molded pulp, paper or the like.
Food packages intended for crisping or browning
food during microwave cooking are disclosed by Fisher
et al, U. S. Patent 4,892,782. ~he packages include
fibers or substrates that are coated or imbibed with
susceptor materials and require the use of much higher
temperatures during cooking to crisp or brown the food.
Brown, U. S. Patent 4,851,273, though not
concerned with food packages for microwavP cooking,
discloses a wide range of pads for use in absorbing
residual oils and grease that may remain on fried food
immediately after the food is removed from the frying
oil. The pad comprises an outer oil-permeable protective
layert which preferably is a woven polypropylene fabric,
and an inner layer of absorbent material, which
preferably is a nonwoven, fibrous polypropylene product.
Brown discloses broad ranges of materials and
characteristics for the pads, but specifi~ally
exemplifies only a pad with the preferred woven
polypropylene outer fabric and the preferred nonwoven
polypropylene absorbent material.
Although known food packa~es for microwave
cooking have bean used with some success, ~urther
improvements are needed to enhance their utility. For
example, the short, weak, polypropylene microfibers of
some absorbing pads in commercial food packages for
microwave cooking often stick to the ~urface of the food
and are pulled out of the pad when the cooked food is
separated from the ~ad. Also, temperatures during
microwave cooking of meats often are high enough (~150C)
to cause softening or even melting of pad fibers. Pads
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made of fibers of ordinary textile decitex usually
require the absence of additives or finishes that are
conventionally used in the manufacture of the fibers. In
this regard, one may use only suhstances approved by the
Federal Food and Drug Adminis~ration for contact with
food, such as the emulsifiers and surface active agents
set forth in 21 CFR Chapter 1 (4-1-88 Edition) Section
178.3400.
It is an object of this invention to provide an
1~ improved microwavable food package wherein the above-
mentioned shortcomings of known packages may be
eliminated or greatly reduced.
SUMMARY OF THE INVENTION
The present invention provides an improvement in
a known package for microwave cooking of food. The known
package contains food resting on a grease-absorbing pad
and has a microwave-transparent film portion through
which microwave energy can pass to cook the food. In
accordance with the improvement of the present invention
the pad has a needle-punched core layer that
weighs 125 to 250 g/m2 and consists essentially of
polyester staple fibers of 1 to 6 dtex and 2.5 to 10 cm
length, and a porous outer layer, intended for being in
contact with the food, that weighs 15 to 25 g/m2,
consists essentially of spunbonded continuous polyester
filaments of 1 to 6 dtex, and is bonded to the
needle-punched staple fiber core layer, and
the pad has a total thickness of 2 to 6
millimeters, preferably 2~5 to 3 mm, and an oil
absorption capacity of at least 0.2 g/cm2, preferably at
least 0.25 g/cm2.
In one embodiment of the invention, the outer
layer and the core of the pad are thermally sealed at
their edges. In another embodiment~ the needle-punched
core layer is bounded on its upper surface by a ~irst
porous spunbonded polyester fabric and on its lower
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surface by a second porous spunbonded polyes~er fabric,
the edges o~ the upper and lower fabrics extending beyond
the edges of the needle-punched core layer and the
extending edges of the two porous fabrics being heat
sealed to each other to completely enclose the
needle-punched core layer. In still another embodiment
having an upper and a lower spunbonded outer layer, the
outer layers and the core layer are hea~ sealed together
at their edges.
In further preferred embodiments of the
invention, the core layer of the grease-absorbing pad of
the food package of the invention has about 15 to 45
needle punches per cm2, most preferably 35 to 40~cm2;
outer layers are point bonded with a pattsrn of discrete
small areas covering 25 to 45~, most preferably 30 to
40%, of the total outer surface area of the pad; and the
absorption capacity of the pad for oil amounts to at
least 10 times the total weight of the pad.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be better understood by
referring to the attached drawings wherein:
Figure 1 is a perspective view with a partial
cut-away of a prior-art microwavable food package 10, in
which a stack of bacon slices 12 in shingled arrangement
with separating sheets 1~ between each pair of slices, is
supported on "absorbent blotter" ti.e., grease-absorbing
pad) 16 which ~omprises perforated layer 18 atop
absorbent layer 20, the stack of bacon slices and the
absorbent blotter being contained between top wrap film
22 and bottom wrap film 24, which films are sealed
togather at seal 26;
Figure 2 is a detailed vertical cross-section at
3-3 of Figure 1 of the prior-art food package 10;
Figure 3 is a grease-absorbing pad 30, intended
3~ for use in a improved ~icrowavable food package of the
invention, having a needle-punched core layer 32 of
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polyester staple ~ibers bonded to a porous spunbonded
polyester nonwoven upper layer 34 and the edges of both
layers bPing heat sealed at seal 35;
Figure 4 is a cross-section of another pad 40
intended for use in a food package of the invention,
having an upper porous spunbonded layer ~4 and a lower
porous spunbonded layer 46 thermally bonded to
needle-punchPd polyester staple fiber core layer 42, the
edges of all three layers being being heat-sealed to form
seal 45 which thereby encloses the needle-punched core
layer; and
Figure 5 is a cross-section of still another a
pad 50 for use in the present invention, the pad having
upper and lower layers 54 and 56 respectively extending
beyond the edges of core layer 5~, the edges of the upper
and lower layers 54 and 56 being heat sealed together at
seal 55 to completely enclose core layer 52.
Each of pads 30, 40 and 50 are intended as
replacements for prior-art absorbent grease-absorbing
blotter 16 of Figure 1 to form an improved microwavable
food package of the invention.
DETA:[~ED DE~SCRIPTION OF P~EFE~RED l~!-Dl~:NTS
The following descriptions of preferred
embodiments are intended to illustrate the invention, but
not limit its scope. The scope of the invention is
defined by the appended claims.
The present invention is an improvement in a
known food package for microwave cooking. In the known
package, food resting on a grease-absorbing pad is
enclosed in a wrapping that has a film portion through
which microwave energy can pass to cook the food. An
example of such a prior-art food package for microwave
cooking is shown in attached Figures 1 and 2 and in
Monforton et al, U. S. Patent 4,786,513, the disclosure
3~ of which is incorporated herein by reference.
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In accordance with the improvement of the
present invention, the grease-absorbing pad comprises a
core layer of needle-punched staple polvester fibers and
a porous outer layer of spunbonded continuous polyester
filaments. The polyester fibers and filaments usually
have a melting temperature of at least 450F (222~).
The high melting temperature of the polyester fibers,
compared to that of the polyolefin fibers of the
absorbers of commercially used food packages for
microwave cooking, permits higher cooking temperatures
without the food ~ecoming stuck to the absorber pad.
Usually, the core layer of the grease-absorbing
pad is formed from a loose web of staple fibers of
polyethylene terephthalate. The polyester fibers
generally have a dtex in the range of 1 to 6, preferably
1.25 to 1.75, and a length in the range of 2.5 to 10 cm,
preferably 3 to 4 cm. A mixture of polyester staple
fibers, within these decitex and length ranges~ can be
used for the core layer. Any finishes on the fibers are
consistent with the requirements of Federal Food and Drug
Administration regulations. Polyester staple fibers
suitable for use in the present invention are available
commercially; for example, Type-lOB DacronR sold by
E. I. du Pont de Nemours ~ Co., Wilmington, ~elaware.
The loose staple polyester fiber web, which
usually has a weight in the range of 125 to 250 g/m2, can
be prepared by conventional carding, air laydown,
Rando-Webber or like techniques. The loose web is
consolidated by needle-punching to form an entangled web.
Needle-punch densities are usually in the range of about
15 to 45 per cm2, preferably 35 to 40/cm2.
The grease-absor~ing pad for use in the present
invention has a porous outer layer which is a spunbonded
nonwoven fabric of continuous polyester filaments. The
filaments usually have an average decitex in the range of
1 to 6. The weight of the spunbonded porous fabric is
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usually in the range of 15 to 25 g/m2. Preferably, the
nonwoven outer fabric contains a minor fraction of
polyester filaments that have a melt temperature ~hat is
somewhat lower ~e.g., 10-~5C) than the melt temperature
of the other polyester filaments in the layer and of the
polyester staple fibers in the consolidated web. Such a
preferred outer layer fabric is Style 2250 Reema ~
spunbonded polyester, which is available commercially
from Reemay, Inc., of Old Hickory, Tennessee. The
Reema ~ fabric is porous and has a Frazier Permeability
of about 1100 ft3/min.
In accordance with the invention, the
needle-punched core layer of polyester staple fibers can
be bonded to the porous outer fabric of spunbonded
polyester filaments by any one of several known
techniques. Conventional hot calendering is prsferred,
particularly with a patterned roll that provides a
visible pattern of "point bonds" on the surface of the
bonded articleD Each point bond is a small discrete
bonded area, usually no larger than about 10 mm2.
Generally, point bonds in accordanca with the invention
cover about 25 to 45% of the outer layer surface, impart
cohesion and strength to the structure, and reduce the
porosity of the outer fabric very little.
When the pad is formed with only one outer layer
of porous spunbonded polyester continuous fllament fabric
bonded to the core layer o~ needle-punched polyester
staple fibers, it is preferred to hea~ seal the edges of
the core and the upper layer together, as schematically
depicted in attached Figure 3. Preferably, both faces of
the core layer are covered with porous spunbonded
fabrics. When both faces of the core are so covered, the
edges of khe porous fabrics and the fiber core can be
similarly sealed, as shown in Figure 4. Alternatively,
the upper and lower fabrics can extend beyond the core of
the pad and be sealed together to completely surround the
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core with the outer ~abrics, as shown in Figure 5. The
sealing may be done by a variety of conventional means.
For example, a sonic welder~ a hot wire or a hot knife
may be used. It is preferred to seal the pad layers
while simultaneously cut~ing the pad to size.
The thusly formed grease-absorbing pads
generally have a total thickness in the range of 2 to 6
mm, preferably 2.5 to 3 mm. With these thicknesse~ and
layer weights described above, the pads efficiently
absorb and retain hot grease and oils released from food
during microwave coo~ing. The pads are also sufficiently
supple to permit the food package to be folded in half,
as is often done with commercial packages of bacon.
The porous outer layers oP spunbonded polyester
filaments of the grease-absorbing pad perform several
functions. The outer layers provide a surface on which
the food rests while being displayed or cooked. The
outer layers also prevent short weak fibers from being
pulled out of the core layer when the food is removed
from the packa~e after cooking. Further, the outer
layers provide strength and dimensional stability to the
composite pad, while permitting fluids generated during
cooking to pass readily through the outer layer to be
absorbed and retained in the staple fiber core.
The grease-absorbing pads for use in food
packages made in accordance with the invention can
readily absorb liquid cooking grease and oils amounting
to many times the dry weight of the pad. Usually, the
pad has an oil absorption capacity (measured as described
hereinafter) of at least 0.2 gram per square centimeter
of pad, preferably at least 0.25 g/cm2. Often the
amount of oil absorbed can be ten or more times the dry
weight of the pad.
The examples below further illustrate preferred
embodiments of the invention. Various characteristics of
the grease-absorbing pads and their performance versus
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commercially used known materials are reported. Test
methods for the measurement of the characteristics are
set forth in the following paragraphs.
Unit weight o the various starting layers of
spunbonded fabrics and staple fiber webs are measured in
accordance with ASTM Method D 3776-79 and is reported
grams per square meter. Fabric thickness is measured
with a conventional fabric thickness gauge having a
right-cylindrical foot of 2-inch (~.0~-cm) diameter
bearing a load of 51 grams. Grab tensile strength is
measured with an Instron Tester in accordance with ASTM
Method D 117-80 an is reported in pounds per inch
(Newtons~cm) of sample width. Porosity of the outer
spunbonded fabric layers is determined with a Fabric
Permeability Machine sold by Frazier Precision Inskrument
Co., Gaithersburg, Md., which measures the flow of air
per minute across a square foot of fabric under a
pressure differential of 0.5 inches of water.
Absorption capacity of the grease-absorbing pad
is measured by placing a sample pad measuring ~-inches
long by 4-inches wide (10~16-cm by 10.16-cm) in a deep
dish filled with sufficient vegetable cooking oil (Wesson
Oil) to completely cover the sample for at least one
minute, removing the sample from the oil and allowing the
sample to drain until oil stops dripping from the sample
(usually in less than two minu~es) and then determining
the weight gain of the sample. Absorption capacity is
recorded as weight gain in grams per square centimeter or
as a ratio of weight gain to original weight of the pad.
~AMPLES
The making of two grease-abæorbing pads of
improved food packages in accordance with the invention
is described in Examples 1 and 2. The oil-absorbing
capacity of the pads of the invention is shown to be
greater than that of typical pads from a conventional
commercial food package for microwave cooking of bacon.
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The advantage of improved microwave food packages of the
invention is further demonstrated in Example 3, wherein
the microwave cooking of bacon strips in a package
containing an improved grease-absorbing pad in accordance
with the invention is compared to such cooking of bacon
in a package containing a pad from a commercial microwave
food package. In contrast to the co~mercial pad, the
cooked bacon did not stiek to the pad of the invention
and the pad of th~ invention absorbed more liquefied
lo grease and fat.
~xamples 1 and 2
Two pads were prepared in accordance with the
invention. The s~arting material for the outer porous
fabric of each pad was a 0.5-o2/yd2 (17-g/m2) spunbonded,
continuous polyester ~ilament, nonwoven fabric ~ReemayR
Style 2250). The core layer of each pad was formed from
a needle-punched carded batt of 1.5-denier (1.6-dtex),
1.5-inch-long (3.8-cm) polyethylene terephthalate staple
fibers (~ype-lOB DacronR, sold by E. I. du Pont
de Nemours and Company). The porous outer fabric was
thermally bonded to the staple fiber core layer by
assembling the layers face-to-face and passing the
assembled layers through the nip formed by two coacting,
internally heated, metal rolls. ~he surface of one of
the rolls was smooth. The surface of the other roll had
an engraved pattern of about 150 square-ended nubs
projecting from each s~uare inch of surface (23.3
nubs/cm2). Each side o~ the square cross-section of each
nub measured about 1.5-mm.
~he grease-absorbing pad of Example 1 was
prepared as follows. A carded batt, as described in the
preceding paragraph and wei~hing about 6.2 oz~yd2 (210
g/m2) was consolidated by needling on conventional
equipment with about 250 needle-punches per square inch
~5 (38.6/cm2). The needled batt was placed atop a porous
0.5_oz/yd2 (17-g/m2) spunbonded, polyester fabric (also
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as described in the preceding paragraph). The porous
fabric had been point-~onded at a temperature of 190C
and under a load of 100 pounds per inch of nip width (18
kg/cm) with a pattern of point bonds that resulted in a
visible pattern that covered about 35% of the surface
area of the porous fabric. The two-layer assembly of
porous fabric and needled batt were then passed through
the point-bonding calender with the ~emperature at 155C
under a load of 60 lb/in (10.~ kg/cm) with the needled
web in contact with the patterned roll. The two layers
were thereby combined into a lightly bonded pad of the
invention which weighed 6.7 oz/yd2 (227 g/m2), was
0.115-inch (2.9-~m) thick and had a grab strength of
about 14 lb/in (24.5 Newtons/cm).
A 4 by 4 inch (10.2 by 10.2 cm) oil-absorption
sample of the pad of Example 1, weighing 2.3 grams, was
placed in vegetable oil for five minutes, removed from
the oil and ~hen held vertically for several minutes,
after which t.ime oil had stopped draining from the
sample. A total was 2~.8 grams of oil was absorbed by
the sample, or about 0.25 gramtcm2. The absorbed oil
weighed 10.8 times the dry weight of the pad.
The grease-absorbing pad of Example 2 was
prepared as follows. A carded batt of polyester staple
fibers was consolidated by needliny with 125 punches/in~
(19.4/cm2). The consolidated batt was placed atop a
first Reemay~ Type-2250 spunbonded, continuous polyester
filament nonwoven fabric. A second identical ReemayR
nonwoven polyester fabric was then placed atop the
needled web. The three-layer assembly was passed through
the nip of the calender rolls (as described in the
preceding paragraph) at a temperature of 170C under a
load of about 100 lb/in (~8 kg/cm) to bond the outer
layers to the inner web. The thusly prepared lightly
3~ bonded pad weighed about 6.9 oz/yd2 (234 g/m2), was
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0.12~-inch (3.1-mm1 ~hick and had a grab strength of
about 26 lb/in (46 N/cm).
An oil-absorption test sample of the bonded pad
of Example 2, weighing 2.4 grams, was placed in vegetable
oil for two minutes, removed from the oil and then
allowed to drain for about 10 minutes. The total amount
of oil absorbed was 35.2 grams. This absorption amounted
to about 0.34 grams/cm2 or almost 15 times the dry weight
of the pad.
For compari~on purposPs, two commercial
polypropylsne grease-absorbing pad were removed from two
different microwave cooking packages of bacon ~sold by
Geo. Hormel Co. of 501 16th ~ve. N.E., Austin MN 559121.
The first polypropylene pad sample, designated comparison
Sample A, had a thickness of 0.048 inch (1.2 mm) and a
density of 0.17 g/cm3 and absoxbed 0.09 g/cm2 of oil in
an oil absorption test (an absorption equivalent to 4.4
times the dry weight of the pad). The second commercial
pad sample, designated comparison Sample B, hacl a
thickness of 0.0~0 inch (1.5 mm), a density of 0.15 g/cm3
an~ an oil-absorption capacity of 0.20 g/cm2 ~e~uivalent
to 9.1 times the dry weight of the pad).
The results reported above indicate that, per
unit weight, the pads of Examples 1 and 2 are superior ~n
oil absorption capacity to the tested commercially used
comparison pads.
Example 3
This example compares the performance of food
package containing an grease-absorbing pad in accordance
3~ with the invention with that of polypropylene pad Erom a
commercial microwave cooking food package. The
superiority of the pad of the invention is clearly
demonstrated.
A grease-absorbing pad sample of Example 1,
measuring 5 by 7 1/2-inches (12.7 by l9ol cm) and
weighing 5.8 grams, and 128.6 grams of bacon were placed
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between two sheets of ~ylarR polyester film (sold by
E. I. du Pont de Nemours & Co.). The edges of the sheets
were sealed together to form a closed pouch. The pouch
and its contents were placed in a microwave oven. The
bacon was then microwave cooked for ~ minutes. Then the
pouch and bacon were removed Erom the oven and allowed to
rest undisturbed for about one minute. The end o~ the
pouch was opened, the pouch was tippe~ to about a 45
degree an~le for about 30 seconds and free liquid grease
allowed to drain. The drained liquid weighed 4 grams.
The cooked, slightly-crisp bacon was lightly wetted with
grease. The bacon, which was then removed from the pouch
weighed 23.5 grams (18% of ~ncooked weight). The pad,
when removed from the pouch, weighed 5606 grams. Thus,
52.B grams of grease were absorbed. This absorption was
equivalent to 0.2~ g~cm2 or about 9.1 times the dry
weight of the pad.
A 5.4-gram pad sample, similar to Comparison
Sample B bu~ being about 50% thicker, was packaged with
122.1 grams o~ bacon, as described in the preceding
paragraph. After cooking and handling as above, the
cooked bacon had fused to the pad and was difficult to
remove. The bacon was excessively wetted with grease and
weighed 29.5 grams ~24% of uncooked weight). The excess
free ~rease weighed 5.1 gra~s, and the pad weighed 50.7
grams. Thus, 45.3 grams of grease w~re ab~orbed, or
approximately 0.19 ~/cm2 or about 8.4 times the dry
weight ~f the pad.
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